August 2019 NY Regents Chemistry Exam
35 Which equation represents a conservation of atoms? (1) 2Fe+2O2 →Fe2O3
(2) 2Fe + 3O2 → Fe2O3
(3) 4Fe + 2O2 → 2Fe2O3
(4) 4Fe + 3O2 → 2Fe2O3
Solution: Conservation of atoms means there is an equal number of atoms of the same element on both sides. Please note that a coefficient in front of the molecule gets distributed to all the atoms in that molecule. For example 2Fe2O3 means there are 4 Fe atoms (2*2) and 6 O atoms (2*3).
In equation 4 we have, 4 Fe on both sides, and 6 O on both sides.
Answer: 4
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